Their comment is putting everyone in two buckets, 1 that sits around and watches TV when they get home from work, and 1 that works on personal development in their free time.
What they want to use that personal development is up to them. They could use it to start a non-profit, or learn a new hobby or learn a new skill. But... sitting around watching TV until bed certainly isn't ambitious.
But here's the thing: the "watch TV/self-development" dichotomy exists and keeps existing at every level of actual achievement. There are people who think that lawyers, doctors, and software engineers are underachievers for not becoming CEOs, after all. Lawyers, doctors, and software engineers tend to think people working old-fashioned 9-5 jobs instead of high-level professions are underachievers. People in old-fashioned 9-5 jobs think part-timers are underachievers.
And in the other direction, there are people who think that anyone who merely runs a business and doesn't build an international business conglomerate is an underachiever. There are people who think that running an international business conglomerate instead of a world empire makes you an underachiever.
There's at least a few people who think that running a worldwide empire makes you an underachiever, because you should be trying to become a god!
Sometimes all you have is an impulse to go in a direction, but not a destination. Those are the impulses to go out for, when no actual destination will sate the impulse.